It is well known that effective restraint of a seated vehicle occupant is provided by a lap belt disposed across the lower torso and a shoulder belt disposed diagonally across the upper torso. The lap belt ends are mounted on the vehicle body respectively inboard and outboard the seat to establish the lap belt in a restraining position across the occupant lower torso. The shoulder belt has one end mounted at a low elevation at one side of the seating position and the other end mounted at a high elevation on the opposite side of the seating position to establish the shoulder belt in a diagonal restraining position across the chest and over the shoulder of the seated occupant.
It is generally recognized that the deceleration loads imposed upon the occupant are best managed by restraining the seated occupant within the seat in a manner by which the occupant is both decelerated in unison with the crush of the vehicle body and also decelerated through the additional space available within the passenger compartment while at the same time minimizing interference with the steering wheel or instrument panel.
One well known type of occupant restraint system is the so-called active three-point seat belt system in which the ends of the lap and shoulder belts are mounted on the vehicle body outboard the seat and carry a latch plate which is manually engageable within a buckle mounted on the vehicle body inboard of the seat to retain the lap and shoulder belts in restraining positions respectively across the upper and lower torsos of the occupant. A retractor is associated with at least one of the belt ends. It is characteristic of the aforedescribed active belt system that the retractor removes the slack from the lap belt with the result that the lower torso remains relatively fixed against forward excursion during rapid vehicle deceleration. On the other hand, the upper torso is pivoted forwardly into the shoulder belt and away from the seat back to a forwardly inclined attitude with the head rotated still further forwardly as seen in FIG. 2. The aforedescribed three-point active belt systems have been in use for many years and have been found to provide effective occupant restraint performance.
Another type of occupant restraint is a passive restraint comprised of the combination of a diagonal shoulder belt and a knee cushion. The shoulder belt has an outboard end mounted on the upper rear corner of the door and the inboard end mounted at a low elevation inboard the seat. A retractor winds one end of the belt when the door closes to establish the shoulder belt in restraining position about the upper torso. A knee cushion is mounted on the instrument panel generally forward of the occupant knees for restraint of the lower torso. This type of passive restraint operates on a different theory from the active lap and shoulder belt restraint in that during vehicle deceleration the lower torso moves substantially forward relative the seat until the knees engage the knee cushion. The spool-down effect or tightening of the considerable length of shoulder belt wound upon the retractor permits limited and controlled forward excursion of the upper torso away from the seat in unison with the forward excursion of the lower torso into restraining engagement with the knee cushion. The resultant kinematics of the occupant are comprised of a more generally vertically upright or slightly reclining position shown in FIG. 3 as opposed to the forwardly pivoted upper torso position of FIG. 2 which characterizes the active three-point system. The more upright occupant position of FIG. 3 provides the desirable effect of limiting forward rotation of the head. It is recognized as advantageous in the aforedescribed passive restraint to provide an active lap belt for optimizing the restraint effectiveness in those instances where the vehicle deceleration is not purely in the head-on direction. To this end, it is known to provide a folded over segment of the lap belt having tearaway stitches which will yield at a predetermined level of load to permit the desired forward excursion of the lower torso into engagement with the knee cushion.
Another type of passive occupant restraint is provided by mounting the outboard ends of both the lap and shoulder belts on the door. The inboard belt ends are mounted inboard the seating position. A retractor is provided for winding the belts when the door closes to establish both the lap and the shoulder belts in their respective restraining positions about the occupant.
One variable which is known to influence the restraining effectiveness of both lap and shoulder belts is the anchorage locations of the belt ends on the vehicle body. With regard to arrangement of the lap belt in belt systems of both the active and passive types, it is known that providing the lap belt anchorage at a relatively high elevation rearward the occupant causes the belt to wrap in a generally horizontal attitude about the occupant and is very effective insofar as limiting the forward excursion of the occupant relative the seat but may result in a so-called submarining condition in which the belt rides above the iliac crests of the pelvis and assumes a restraining position overlying the soft abdominal area of the occupant. On the other hand, it is recognized that anchorage of the lap belt ends at a lower elevation relatively more forward causes the belt to assume a more vertical attitude passing over the thighs and effectively overcomes the submarining condition. However, it is reported that a lessened restraining effect may result from this forward location of the lap belt anchorages because of increased forward excursion of the seat occupant.
As a consequence of the conflicting objectives of preventing submarining beneath the belt and limiting forward excursion of the occupant, it has been recognized that the lap belt ends should be anchored in a zone which is not so high and rearward as to cause submarining and yet not so low and forward as to permit forward occupant excursion. To this end, Motor Vehicle Safety Standard, MVSS 210, promulgated by the United States National Highway Traffic Safety Administration specifies that the mounting locations of the lap and shoulder belt ends fall within the permissible range shown by the cross-hatched areas in the drawings.
It is known that the mounting locations specified by MVSS 210 may be inapplicable to passive seat belt systems in which it is necessary to mount the outboard shoulder belt end on the window frame of the door so that the swing geometry of the door automatically moves the shoulder belt between the access and restraining positions. As an example, FIG. 8 shows the outline of the door of a 4-door Chevrolet Chevette and it is noted that the trailing edge of the door adjacent the occupant shoulder falls very close to the forwardmost limit of the acceptable range of anchorage locations. Accordingly, Applicants' assignee petitioned for amendment of MVSS 210 in order to delete the forward limitation on the shoulder belt anchor locations. In consequence of that petition, MVSS 210 was amended to exempt passive seat belt systems from the specified location requirements.
Referring again to FIG. 8, it is noted that the forwardmost limit of the acceptable range for mounting of the lap belt falls well forwardly of the trailing edge of the door, and accordingly does not present any complication with respect to mounting the outboard end of the passive lap belt within the acceptable range of anchorage locations specified by the MVSS 210.
It is also recognized in the prior art that inertia locking seat belt retractors experience some delay in fixing the length of the belt due to the so-called spool down effect caused by the tightening of several layers of belt wound on the reel. It has been recognized that this lockup delay is largest in passive door connected belt systems because a relatively large amount of belt is wound upon the retractor reel when closing movement of the door establishes the belts in the restraining position. The prior art has proposed that this problem of lockup delay be solved by providing a belt clamping device after the belt exits the reel to clamp the belt at a fixed length. Various piston operated belt tensioning devices have also been proposed to forcibly rotate the reel in the belt winding direction.